The most mature technologies for IR scene generation can be classified into three categories: thermal emitter arrays, spatial light modulators, and laser-based projection systems.
Thermal emitter arrays are those scene generators which are based on individually addressable resistively heated arrays. The inherently low emissivities of the semiconductor/metal materials used in these devices reduce the effective black body temperature for any given pixel. The low emissivities are compensated for by higher drive currents that produce the higher temperatures necessary to achieve a desired emittance. However, increased temperatures lead to increased thermal loads that reduce the maximum speed at which the generator may change scenes. Thermal cross talk between adjacent pixels is also increased leading to a reduction in spatial resolution.
Spatial light modulators are devices which spatially modulate incident radiation from IR sources. They include liquid crystal modulators, metallic gratings, and deformable mirror arrays that are typically wavelength limited and, consequently, perform poorly in the IR band. Work is progressing in this area but emphasis is on new materials and processes that are unlikely to compete cost-wise with the thin-film cavity approach of this invention that relies on mature optical technologies.
Laser-based projection systems used steered laser beams to write images directly on the imaging detector array. This technology requires high intensity laser sources that are modulated so the cumulative energy which arrives at each detector pixel is equivalent to that which would come from all the natural scene being modeled. The spatial resolution, thermal resolution, and frame rate of the laser system all depend on the controller which drives the position of the laser beam as a function of time. Such controllers are expensive and software maintenance is a prime concern. While these devices meet very specialized needs, their cost and complexity limit their application.
Thus, in accordance with this invention, a need was discovered in the state-of-the-art for cost effective multi-layered thin-film transducers for arrays of optical fibers that convert electromagnetic radiation, such as visible light, into IR emission.